Patch antennas are common in wireless handheld communication devices due to their low profile structure. Further, patch antennas can be implemented with a virtually unlimited number of shapes, thereby allowing such antennas to conform to most surface profiles. Since modern handheld communication devices are required to operate in multiple frequency bands, multi-band patch antennas have been developed for use in such devices.
For instance, Wen (U.S. Pat. No. 7,023,387) describes a dual-band antenna that comprises a first C-shaped patch antenna structure, and a second C-shaped patch antenna structure coupled to the first patch antenna structure, each patch antenna structure having a respective slot structure. The first patch antenna structure includes a signal feed point, and the second patch antenna structure includes a ground point that is proximate the signal feed point.
On the other hand, planar inverted-F antennas (PIFA) are becoming more common in wireless handheld communication devices due to their reduced size in comparison to conventional microstrip antenna designs. Therefore, PIFA antennas have been developed which include multiple resonant sections, each having a respective resonant frequency. However, since conventional PIFA antennas have a very limited bandwidth, broadband technologies, such as parasitic elements and/or multi-layer structures, have been used to modify the conventional PIFA antenna for multi-band and broadband applications.
These approaches increase the size of the antenna, making the resulting designs unattractive for modern handheld communication devices.
Also, the additional resonant branches introduced by these approaches make the operational frequencies of the antennas difficult to tune. Further, the additional branches can introduce significant electromagnetic compatibility (EMC) and electromagnetic interference (EMI) problems.